The proposed work is directed at an attempt to more fully understand the underlying molecular biology in thrombosis and hemorrhagic diseases. Bovine Ac-globulin (Factor V) is to be isolated by methods developed in this laboratory. The properties of this product are to be studied by protein chemistry technics. Emphasis is to be on the mechanism whereby thrombin, prepared as for crystallization, increases and subsequently decreases Ac-globulin activity. If a peptide(s) is split off, it is to be isolated and its amino acid sequence is to be determined. Coagulase thrombin is to be obtained from purified human prothrombin. The structure is to be ascertained and compared to the structure of classical human thrombin in order to account for the peculiar fact that coagulase thrombin is not sensitive to antithrombin III, heparin, or hirudin, but removes peptides A and B from fibrinogen. Purified chicken prothrombin is to be prepared and the nature of the activation steps produced by the active principal of Echis carinatus venom is to be outlined in terms of the properties of intermediates. The primary structure of the purified chicken thrombin is to be determined by using an automated amino acid sequencer. A question is whether avian thrombin will show homology with mammalian thrombin. Divergence of mammals and birds occurred about three hundred million years ago.